Spiral drive fastener with engagement ramp

ABSTRACT

The fastener of this application is designed to facilitate the insertion of rotating power driven tools into the fastener recess. The recess of this fastener generally uses spirally configured driving surfaces and is formed in a counterbore in the upper surface of the fastener. The driving lobes have upper surfaces that are depressed a distance into the counterbore. A ramp surface is formed on each of the upper surfaces that causes a spinning bit to fall into the recess in an engaged manner. The ramp surfaces are constructed with both removal and installation ramp portions.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of, and is a divisional of U.S.application Ser. No. 10/960,401 filed Oct. 7, 2004 now U.S. Pat. No.7,255,522 which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates in general to drive systems for threadedfasteners, tools for their manufacture, and drivers for applying torqueto such fasteners. More specifically this application relates tofasteners that employ winged type drivers. In particular fastenershaving a recess that provides spiral driving surfaces and furtherwherein said recess is designed to facilitate engagement of a rotatingdriver.

2. Brief Description of Related Developments

Threaded fasteners commonly used in industrial applications typicallyare driven by power tools at high speeds and under high torque loads.Such conditions present difficult design considerations, particularlywith respect to the drive systems and, more particularly, with threadedfasteners having a driver engageable recess in the fastener head.Ideally, such a drive system should be easily manufactured, both as torecess and head geometry as well as to associated tooling for formingthe fastener head and drivers for engaging the recess. The strength ofthe head of the fastener should not be adversely affected by the recess.The driver should be easily insertable into and easily withdrawn fromthe recess. The driver and recess, when mated, should distribute thestress loads uniformly to avoid formation of highly localized regions ofstress that might result in deformation of the recess, or driver, orboth, leading to premature failure of the drive system.

The drive system should resist cam-out of the driver from the recesswhen the fastener is driven. In many applications, it is very importantthat the fastener must be capable of withstanding several cycles, as inapplications where the fasteners must be removed in order to repair orreplace parts or to remove and replace access panels. The fastener drivesystem ideally should be capable of such repeated cycling, particularlyin environments where the recess may become contaminated, painted,corroded or otherwise adversely affected in use. In such environments,it is essential that the drive system maintain driving engagement whileapplying torque in a removal direction. It may be necessary for thedrive system to be capable of applying even higher levels of torque whenremoving the fastener, as may occur when the fastener is over-torquedduring initial assembly, or where corrosion develops at the interface,at the engaged threads, or if thermal cycling of the assembledcomponents has placed increased stress on the fastener. Where one ormore of these, and other, characteristics may present competingconsiderations, compromises of one in favor of another may be made.

A variety of recess and driver configurations are in common use,including a number of cross-recesses, such as those described in U.S.Pat. No. 24,878 (Smith et al.); U.S. Pat. No. 3,237,506 (Muenchinger)and U.S. Pat. No. 2,474,994 (Tomalis). Other fastener geometries includemulti-lobe geometries of the type described in U.S. Pat. No. 3,763,725(Reiland) and ribbed drive systems as described in U.S. Pat. No.4,187,892 (Simmons). Also among the common recess configurations is theAllen system which is essentially a straight walled hexagonally shapedsocket receptive to a similarly shaped driver.

With the exception of the ribbed systems, the walls and faces of thedriver and recess typically are designed to fit closely with each otherin an effort to achieve face-to-face contact of the driving and drivensurfaces. With cross-recess fasteners, such face-to-face engagement canoccur only, if at all, when the driver is properly aligned and seatedwithin the recess. As a practical matter, however, in order to enablethe driver to be inserted into the recess, there necessarily must besome clearance between the two.

The necessity for such clearance is even more critical with recesseshaving substantially vertical drive walls, as in the Reiland '725 patentand Allen head systems. In all of these systems, the practical result ofthe necessity for such clearance is that substantial face-to-face, broadarea contact between the driver and recess surfaces is seldom achieved,if at all. With most drive systems for threaded fasteners, the drivermates with the recess in the head in a manner that results in point orline contact rather than face-to-face broad area contact. The actualarea of contact typically is substantially less than full face-to-facecontact. Consequently, when torque is applied by the driver, the forcesapplied to the screw head tend to be concentrated in localized areaswith resulting high localized stresses. Such localized high stress canplastically deform the recess, forming ramps or other deformationsresulting in premature, unintended disengagement of the driver from therecess.

The foregoing difficulties have been recognized in the art. For example,U.S. Pat. No. 2,248,695 (Bradshaw) discloses a screw head and driverarrangement in which the driving and driven faces of the driver andfastener, respectively, are curved and located eccentrically withrespect to the screw axis. In the Bradshaw fastener, any “suitablecurvature” such as circular or log spiral may be used as long as it isoriented to bind or lock together by frictional engagement.Notwithstanding Bradshaw's teachings, later fastener drive systems, asthose referred to above, do not appear to have adopted the Bradshawteaching of relying on frictional engagement.

A drive system for maximizing the engageable surface area between thedriver and recess is described in U.S. Pat. No. 5,957,645, which iscommonly owned with the subject application. The disclosure of the '645patent is incorporated in this application by reference. The recess anddriver of the '645 patent are constructed with spirally configuredengaging surfaces.

The advantages of the invention described in the '645 patent areachieved by configuring the driving and driven surfaces of the driverand fastener, respectively, to conform to a segment of a spiral and,particularly, in a spiral configuration that enables a substantial andgenerous clearance between the driver and the recess during insertionand removal of the driver but in which the fully seated driver ispermitted to rotate to take up that clearance. The spiral configurationsof the drive walls of the driver and the driver-engageable walls of therecess are such that when the spiral walls engage, they do so over arelatively broad area thereby applying and distributing the stress overthat broad area. The spirally configured driving and driven walls areoriented to direct a major portion of the applied torque substantiallynormal to the fastener radius with little, if any, reliance onfrictional, near-tangential engagement.

While each of the multiple lobed drive systems have some similaritiesand differences, it is common among them that, as the engagement of therecess and driver is optimized, the insertion of the driver becomes moreproblematic. Relatively precise alignment between the driver and lobesis required in order to obtain quick, full engagement. This isespecially critical in production and other environments where thedriver is generally rotating as it is being engaged with the recess of afastener. In the rotating mode and even in simple manual installations,the failure of proper alignment of the driver in the recess may generatedeformation of the fastener head and even destruction of the fastener.There are several solutions to this problem in the prior art.

U.S. Pat. Nos. 277,353, 3,253,625, and 3,620,106 describe a varietyearly insertion enhancing recess configurations that apply to specificdriver designs. More recently U.S. Pat. No. 5,171,117 issued to Seidl in1992 and describes a guide surface 27 for adaptation to a multilobularrecess. The guide surface of this system extends over the upper surfaceof a lobe and gradually slopes downward in the direction of installationof the fastener. This configuration is difficult to manufacture and onlyfacilitates installation. It is counter productive in engaging driversin the removal direction of the fastener.

It is a purpose of this invention, to construct a surface on the lobe ofa recess that is easily manufactured and provides ramps in bothdirections of fastener rotation.

SUMMARY OF THE INVENTION

The fastener of this application is designed to facilitate the insertionof rotating power driven tools into the fastener recess. The recess ofthis fastener generally uses spirally configured driving surfaces and isconstructed having four radially inward protruding lobes that define thewings of the recess. Lobes are formed in a counterbore in the uppersurface of the fastener and each has an upper surface that is depresseda distance into the counterbore. A ramp surface is formed in the uppersurfaces that causes a spinning bit to fall into the recess in anengaged manner. The ramp surface is constructed with both removal andinstallation ramp portions. The removal ramp portion extends from anapex to a trailing edge in a sector of predetermined circumference.Removal ramp portion is formed to decline at a compound angle generallydownward, radially inward towards the axis of the fastener and generallydownward in the removal direction. An installation ramp portion extendsfrom the apex of the ramp surface to its leading edge in a sector ofanother predetermined circumference. The installation ramp portion isformed to decline at a compound angle generally downward radially inwardtowards the axis of the fastener and generally downward in theinstallation direction.

In this manner a fastener recess is provided that may be manufacturedusing familiar techniques and that facilitates engagement in both theinstallation and removal directions.

BRIEF DESCRIPTION OF THE DRAWINGS

The fastener of this invention is explained in more detail below withreference to the accompanying drawing, in which:

FIG. 1 is perspective view of a flat head screw having a spirallyconfigured recess;

FIG. 2 is a cross sectional view of a flat head screw having a rampedlobe surface according to this invention;

FIG. 3 is a perspective sectional view of a fastener having theengagement ramp of this invention;

FIG. 4 is a perspective view of a punch for use in making the recess ofFIG. 2;

FIG. 5 is a top view of the punch of FIG. 4;

FIG. 6 is a side sectional view of the punch of FIG. 4 taken along thesections lines 8-8 of FIG. 5;

FIGS. 7 a-7 e illustrate the steps in the construction of a punch foruse in forming the recess of this invention; and

FIGS. 8 a-8 b illustrate the cold forming of the recess of thisinvention utilizing the punch of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 illustrates an exemplary threaded fastener 10 having a shank 12with threads 14 formed at one end and a head 16 with a recess 18 formedat the other end. The head 16 may be formed in a conventional two-blowheader machine in which the end of the wire or other material from whichthe fastener is made is supported in a die of the header machine and itshead end is impacted, first with a punch that partially forms the head,and then with a finishing punch that finishes the head and forms thedriver-engageable recess.

The recess 18 is illustrated as having a central portion 20 and aplurality of radially outwardly extending wings 22. The recess in theembodiment of FIG. 1 is formed so that each of its wings 22 has aninstallation wall 24 (assuming a right-handed thread 14) and a removalwall 26. The installation wall 24 and removal wall 26 preferably areformed to be substantially vertical, defining or closely approximating acylindrical surface parallel to the longitudinal axis of the screw. Thebottom of the recess may be defined by a conical bottom wall 28. Theradially outer end of each wing may be contoured to provide a smoothlycurved transition 30 between the installation wall 24 and removal wall26 of the wing. The recess also includes an inner transition wall 32between the installation wall 24 of one wing 22 and the removal wall 26of the next adjacent wing 22.

It should be understood that the invention may be incorporated inthreaded fasteners in a wide variety of configurations includingrecesses generally of the cruciform type and those having more or lessthan four wings as shown. Although the subject invention is describedwith reference to a spiral type engagement, this invention may beequally effective in recesses having other engagement schemes.

The fastener of this invention is generally similar to that shown inFIG. 1, but includes the modifications shown in FIG. 2. As stated abovethe fastener 10 of this application is designed to facilitate theinsertion of rotating power driven tools into the recess 18. The recess18 of the fastener 10 of this invention is best shown in the sectionalview of the attached FIG. 2 and in the perspective view of FIG. 3.Fastener 10 comprises head 16 and shank 12. Head 16 is constructed witha recess 18 formed in upper surface 7 of the head 16. Recess 18 isconstructed, for example, having four radially inward protruding lobes 3that define the wings 22 of the recess.

In the fastener of this invention lobes 3 are formed in a counterbore 2in upper surface 7 and have an upper surface 8 that is depressed adistance d into the counterbore 2.

Each ramp surface 1 is similarly formed in the recessed upper surface 8of the lobes 3, as shown in FIGS. 2 and 3, and is constructed with anramp 1 that extends over a sector of approximately 90°. The ramp 1 andthe counterbore 2 cause a spinning bit to fall into the recess in anengaged manner. The ramp 1 of lobe surface 8 is constructed with bothremoval and installation ramp portions 5 and 6 respectively.

Removal ramp portion 5 extends from the apex 9 of ramp 1 to trailingedge 11 (using a clockwise rotation 40 of FIG. 1 as a reference) to forma sector of circumference x. Removal ramp portion 5 is formed to declineat a compound angle generally downward, radially inward towards the axisof the fastener and generally downward in the removal direction(counterclockwise direction 41 in FIG. 1) at an angle A, as shown inFIG. 2. Angle A will be in the range of 1° to 2°.

Installation ramp portion 6 extends from the apex 9 of ramp 1 to leadingedge 15 (using a clockwise rotation 40 of FIG. 1 as a reference) to forma sector of circumference y. Installation ramp portion 6 is formed todecline at a compound angle also generally downward, radially inwardtowards the axis of the fastener and generally downward in theinstallation direction (clockwise direction 40) at an angle B, as shownin FIG. 2. Angle B will be in the range of 2° to 6°.

In the embodiment of FIG. 2, ramp portion 6 extends for a sector ofsubstantially 60° and ramp 5 extends for a sector of substantially 30°.This will change according to the number of lobes, but in general therelative size of the ramp portions will be roughly 2 to 1 for ease ofmanufacture.

Counterbore 2 assists in the engagement of the driver by acceleratingthe engagement of the driver as it approaches the ramp 1. Counter bore 2is constructed at a minimum depth d, at the apex 9 of ramp 1, which willvary depending on the size of the fastener, for example, 0.0044 inchesfor a fastener having a recess size MT-1. The ramp portion 6 declines atangle B from the apex 9 in the installation direction to a depth d₁. Theramp portion 5 declines at angle A in the removal direction to a depthd₂.

A punch 50 is shown in FIGS. 4-6 and is constructed for use in coldforming the recess of this invention into a fastener blank by pressingunder high pressure in a well known manner. Punch 50 is formed withlobes 52 for forming the wings 22 of the fastener 10 shown in FIGS. 2and 3. Lobes 52 extend outward from surfaces 53 that are constructed toform the counter bore 2 of fastener 10. Surfaces 53 are contoured as amirror image of the ramp portions 5 and 6 to form the ramp 1 of fastener10.

To accomplish this, surfaces 53 are constructed with portion 55extending from the apex 59 of surface 53 to tip 61 of the adjacent lobe52, in the clockwise direction in FIG. 5, to form a sector ofcircumference x. Portion 55 is formed to incline at a compound anglegenerally upward, radially inward towards the axis of the punch andgenerally upward towards tip 61 at angle A, as shown in FIG. 2. Angle Awill be in the range of 1° to 2°.

In addition a portion 56 extends from the apex 59 of surface 53 to tip62 of the adjacent lobe in the counterclockwise direction of FIG. 5 toform a sector of circumference y. Portion 56 is formed to incline at acompound angle generally upward radially inward towards the axis of thepunch and generally upward towards tip 62 at an angle B, as shown inFIG. 2. Angle B will be in the range of 2° to 6°. In the embodiment ofFIG. 5, portion 56 extends for a sector of substantially 60° and portion55 extends for a sector of substantially 30°. This will change accordingto the number of lobes, but in general the relative size of the rampportions will be roughly 2 to 1 for ease of manufacture.

Punch 50 is constructed, as shown in FIGS. 7 a-7 e, and is then used tocold form the fastener 10 in a well known manner as shown in FIGS. 8 aand 8 b.

To construct punch 50, a wire EDM operation is used to construct a dieor hob 70, as shown in FIGS. 7 a-7 e, for cold forming a punch fromwhich the recess of fastener 10 can be made. The hob 70 is constructedfrom a blank 71 of steel bar stock, for example, one inch long by oneinch in diameter, that is centerless ground to a tolerance of one inch+0.0005/−0.0000. The ends of the blank need to be parallel and square tothe outside diameter. Close tolerances are necessary to ensure asuccessful wire EDM operation. As shown in FIG. 7 a, a central bore 72is drilled axially in the blank 71 at a diameter less than the rootdiameter of recess 18.

The fully dimensioned and drilled blank 71 is then positioned in a wireEDM fixture with the wire inserted through the bore 72. The wire EDM isprogrammed to cut out a block of material to form a die cavity 73 in theshape of the spiral recess 18, as shown in FIG. 2. To achieve theportions 55 and 56 on each lobe in punch 50, an EDM probe 80 is machinedwith the contours of surfaces 53, as shown in FIG. 7 c. Surfaces81,82,83 and 84 are machined onto probe 80. In order to obtain therequired shape for the ramp surfaces, the surfaces 81-84 are machined atcompound angles of 9 and 15 degrees.

Using probe 80, as shown in FIG. 7 d, a counterbore 74 having rampsurfaces 75 and 76 on each lobe can be formed. Die cavity 73 of hob 70is then complete with the shape of the recess 18 of fastener 10, asshown in FIG. 7 e. Hob 70 is then used to make punch 50 by pressing.Fastener 10 can be made by cold forming a blank using the punch 50 asshown in FIGS. 8 a and 8 b.

While the invention has been described with reference to specificembodiments, the description of the specific embodiments is illustrativeonly and is not to be construed as limiting the scope of the invention.Various other modifications and changes may occur to those skilled inthe art without departing from the spirit and scope of the invention, asdefined by the claims.

1. A method of making a punch for forming a recess in the top surface ofthe head of a fastener, said recess having multiple radially inwardextending lobes that define spirally configured driving surfaces, saiddriving surfaces extending substantially axially, from outward facingtop surfaces of the lobes towards the bottom of the recess, said drivingsurfaces constructed for engagement with a mating drive tool forrotating said fastener in installation and removal directions about alongitudinal axis, said method comprising the steps of: forming asubstantially cylindrical, axially aligned, bore in a die blank, formingmultiple lobes in said bore to define the multiple driving surfaces ofthe fastener recess; constructing a non-driving ramp surface on each ofsaid multiple lobes of said die on outward facing surfaces thereof, saidramp surfaces being recessed a predetermined depth in a counterbore insaid bore, each of said ramp surfaces further comprising: aninstallation ramp portion extending radially inward andcircumferentially in the installation direction from an apex of saidramp surface, wherein said installation ramp portion declines from theapex at a compound angle both radially and circumferentially; and aremoval ramp portion extending radially inward and circumferentially inthe removal direction from the apex of said ramp surface, wherein saidremoval ramp portion declines from the apex at a compound angle bothradially and circumferentially; wherein said installation ramp portionand said removal ramp portion are adapted to urge a rotating drive toolinto mating engagement with the drive surfaces in either theinstallation or removal directions; and cold forming the punch bypressing a punch blank into said die.
 2. The method according to claim1, wherein the step of constructing a ramp surface on each of saidmultiple lobes on outward facing surfaces thereof further comprises thesteps of: constructing a substantially cylindrical wire EDM probe shapedto fit within the counterbore, said probe having an engaging surface;constructing a series of forming surfaces matching the number of lobeson said engaging surface to form the compound angles of the installationand removal ramp portions.
 3. The method according to claim 2, whereinthe step of constructing a series of forming surfaces further comprisesthe step of machining four forming surfaces at a compound angle of 9 and15 degrees.
 4. A punch for forming a recess in the top surface of thehead of a fastener, said recess having multiple radially inwardextending lobes that define spirally configured driving surfaces, saiddriving surfaces extending substantially axially, from outward facingtop surfaces of the lobes towards the bottom of the recess, said drivingsurfaces constructed for engagement with a mating drive tool forrotating said fastener in installation and removal directions about alongitudinal axis, said punch comprising: a punch head extending outwardfrom a shank to a tip having lobes arranged to form the spirallyconfigured driving surfaces, said punch head having a first diameter atthe shank and further comprising; a substantially cylindrical, axiallyaligned, base portion having a second diameter, said base portionconstructed outward on the shank of the punch wherein, said seconddiameter is less than said first diameter, and further wherein saidlobes project outward from said base portion to the tip and extend inthe radial direction to the second diameter, said lobes forming wingshaped surfaces facing outward on said base portion, between each lobe;a non-driving ramp surface constructed on each of said wing shapedsurfaces, each of said ramp surfaces further comprising: an installationramp portion extending radially inward and circumferentially in theinstallation direction from a trough of said ramp surface, wherein saidinstallation ramp portion inclines from the trough at a compound angleboth radially and circumferentially; and a removal ramp portionextending radially inward and circumferentially in the removal directionfrom a trough of said ramp surface, wherein said removal ramp portioninclines from the trough at a compound angle both radially andcircumferentially.
 5. A punch, according to claim 4, wherein saidinstallation ramp portion forms a sector of said base extending in afirst predetermined circumference and said removal ramp portion forms asector of said base extending in a second predetermined circumferenceand wherein said first sector circumferences is greater than said secondsector circumference.
 6. A punch, according to claim 5, wherein theratio of said first sector circumferences to said second sectorcircumference is substantially 2 to
 1. 7. A punch, according to claim 5,wherein said first sector circumference is 60° and said second sectorcircumference is 30°.
 8. A punch, according to claim 4, wherein theinstallation ramp portion inclines circumferentially at a predeterminedangle.
 9. A punch, according to claim 8, wherein said predeterminedangle is in the range of 2° to 6°.
 10. A punch, according to claim 4,wherein the removal ramp portion inclines circumferentially at apredetermined angle.
 11. A recess for a fastener, according to claim 10,wherein said predetermined angle is in the range of 1° to 2°.